350 HANDY-BOOK OF HUSBANDRY. 



which, for this reason, may be assumed to be particularly grateful 

 for a supply of it in a soluble state. Silica, indeed, if at all capa- 

 ble of producing a beneficial effect, ought to be useful to these 

 crops, either by strengthening the straw or stems of graminaceous 

 plants, or otherwise benefiting them ; but after deducting the 

 amount of silica from the total amount of mineral matters in the 

 wheat produce from one acre, only a trifling quantity of other and 

 more valuable fertilizing ash-constituent of plants will be left. 

 On comparing the relative amounts of phosphoric acid and potash 

 in an average crop of wheat and a good crop of clover-hay, it will 

 be seen that i acre of clover-hay contains as much phosphoric 

 acid as ij acres of wheat, and as much potash as the produce from 

 5 acres of the same crop. Clover thus unquestionably removes 

 from the land very much more mineral matter than is done by 

 wheat J clover carries off the land at least three times as much of 

 the more valuable mineral constituents as that abstracted by the 

 wheat. Wheat, notwithstanding, succeeds remarkably well after 

 clover. 



" Four tons of clover-hay, or the produce of an acre, contain, 

 as already stated, 224 lbs. of nitrogen, or, calculated as ammonia, 

 272 lbs. ' 



"Assuming the grain of wheat to furnish 1*78 per cent, of 

 nitrogen, and wheat-straw "64 per cent., and assuming, also, that 

 1,500 lbs. of corn and 3,000 lbs. of straw represent the average 

 produce per acre, there will be in the grain of wheat per acre 26*7 

 lbs. of nitrogen, and in the straw 19*2 lbs., or in both together 46 

 lbs. of nitrogen ; in round numbers, equal to about 55 lbs. of 

 ammonia, which is only one-fifth the quantity of nitrogen in the 

 produce of an acre of clover. Wheat, it is well known, is speci- 

 ally benefited by the application of nitrogenous manure, and as 

 clover carries off so large a quantity of nitrogen, it is natural to 

 expect the yield of wheat, after clover, to fall short of what the 

 land might be presumed to produce without manure, before a crop 

 of clover was taken from it. Experience, however, has proved 

 the fallacy of this presumption, for the result is exactly the oppo- 

 site, inasmuch as a better and heavier crop of wheat is produced 

 than without the intercalation of clover. What, it may be asked 

 is the explanation of this apparent anomaly ? 



" In taking up this inquiry, I was led to pass in review the cele- 

 brated and highly important experiments undertaken by Mr. 

 Lawes and Dr. Gilbert, on the continued growth of wheat on the 

 same soil for a long succession of years, and to examine, likewise, 

 carefully, many points, to which attention is drawn, by the same 



